When I resize images, I do it in as small as increments as I can allow for time-wise. For example:
Your image starts out as a 2048x 1536 pixel image, and you require it's width to be 700 Pixels (for online display in these forums), resize it's horizontal axis by a size of 100 pixels smaller for each increment while maintaining the image's original proportions (4:3). Also, to make things simpler, the first time you resize the image 'round' the image's axis of to a "100's" figure- in this example; the first time you resize it to 2000x 1500 Pixels.
If you have plenty of time to spare, resize it at 50 pixels on the axis each time instead. I use Microsoft Picture It9 to resize my images, which simplifies this proccess. (I dont have access to Adobe photoshop yet).